Pumps utilized for high volume, high pressure pumping of abrasive fluids such as drilling mud utilized in drilling hydrocarbon wells, are subject to high maintenance problems. A pump construction which simplified driving of the pumping elements from a motor while minimizing the load on the motor, which minized wear on the valves and seals, and which enabled a more compact and simplified pumping system to be constructed, would be of considerable value in pumping drilling mud under high pressure as well as in other pumping applications.